Circuit for Clamping Current in a Charge Pump

ABSTRACT

A circuit for clamping current in a charge pump is disclosed. The charge pump includes switching circuitry having a number of switching circuitry transistors. Each of first and second pairs of transistors in the circuit can provide an additional path for current from its associated one of the switching circuitry transistors during off-switching of that transistor so that a spike in current from the switching circuitry transistor is only partially transmitted through a path extending between the switching circuitry transistor and a capacitor of the charge pump.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/405,645, filed Feb. 27, 2012, which is a continuation of U.S.application Ser. No. 13/032,175, filed Feb. 22, 2011, now U.S. Pat. No.8,149,032, which is a continuation of U.S. application Ser. No.11/606,827, filed Nov. 30, 2006, now U.S. Pat. No. 7,915,933.

The entire teachings of the above applications are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

As will be appreciated by those skilled in the art, a charge pump can becharacterized as a circuit that uses capacitors to create either ahigher or lower voltage. Charge pumps are used in a variety of differentapplications such as, for example, applications involving Delay LockedLoops (DLLs) and Phase-Locked Loops (PLLs).

With respect to PLLs, a charge pump can be used to provide a controlvoltage applied to a Voltage Controlled Oscillator (VCO). Typically, aPLL includes a phase detector, a loop filter coupled to the output ofthe charge pump, an amplifier, and a VCO interconnected in a knownmanner to form a feedback system. The charge pump converts logic levelpulses generated by the phase detector into current pulses which are fedto the loop filter. The loop filter integrates the current pulses toproduce a control voltage for the VCO.

With respect to DLLs, a charge pump can be used to provide a controlvoltage for a Voltage Control Delay Line (VCDL) of the DLL. As will beappreciated by those skilled in the art, in certain types of devices(for example, DRAM devices) a DLL can be used to change the phase of aclock signal. In this regard, a DLL includes a delay chain composed ofnumber of delay gates connected in series (in a daisy chain manner).

Those skilled in the art will appreciate that, besides thoseapplications involving DLLs and PLLs, there will be other applicationswhere, for example, a charge pump will be employed in an electroniccircuit having an accurately controlled current source/sink for voltageregulation on a filter or reservoir capacitor.

SUMMARY OF THE INVENTION

According to one example embodiment, there is a method for clampingcurrent in a charge pump. The charge pump includes switching circuitryand a capacitor. The charge pump defines first and second paths. Foreach of the first and second paths, a selected one of the followingholds i) current is transmitted to the capacitor; and ii) current isreceived from the capacitor. At least one parasitic spike in currentfrom at least one of a number of transistors of the switching circuitryis generated during switching off of the at least one transistor. The atleast one parasitic spike is dissipated after elapse of a short periodof time. The method includes the step of providing at least one controlsignal that causes the switching off of the at least one transistor whenthe at least one control signal changes from a first value to a secondvalue. The method also includes the step of opening an additional pathfor the current from the at least one of the transistors when the atleast one control signal changes from the first value to the secondvalue in order that the at least one parasitic spike is only partiallycommunicated through a selected one of the first and second paths. Themethod also includes the step of closing the additional path after theadditional path has been open for the short period of time.

According to another example embodiment, there is a circuit for clampingcurrent in a charge pump. The charge pump includes switching circuitryand a capacitor, and the charge pump defines first and second paths. Foreach of the first and second paths, a selected one of the followingholds i) current is transmitted to the capacitor; and ii) current isreceived from the capacitor. At least one parasitic spike in currentfrom at least one of a number of transistors of the switching circuitryis generated during switching off of the at least one transistor. Thecircuit includes first and second pairs of transistors, each of thetransistors supporting on and off states, and each including a controlelectrode to permit transition between the states to be controlled. Oneof the first pair of transistors is electrically connected to a first ofthe transistors of the switching circuitry through a first node. Thefirst path extends through the first node. One of the second pair oftransistors is electrically connected to a second of the transistors ofthe switching circuitry through a second node. The second path extendsthrough the second node. The circuit also includes first delayintroducing inverter circuitry and second delay introducing invertercircuitry, each of the first inverter circuitry and the second invertercircuitry having an input signal connected to the control electrode ofthe one of the respective pair of transistors and a delayed outputsignal connected to the control electrode of the other of the respectivepair of transistors. For a moment when the switching off occurs, boththe input signal and the delayed output signal have values that producethe on state. At least one of the first and second pairs of transistorsprovide an additional path for the current from the at least one of thetransistors during the switching off so that the at least one parasiticspike is only partially communicated through any paths to the capacitor.

According to another example embodiment, there is an apparatus includinga charge pump. The charge pump includes a number of switchingtransistors, a current clamping circuit and a capacitor. The charge pumpdefines first and second paths. For each of the first and second paths,a selected one of the following holds i) current is transmitted to thecapacitor; and ii) current is received from the capacitor. One of theswitching transistors is located on a selected one of the first andsecond paths. The switching transistor generates a parasitic spike incurrent when it switches off. The parasitic spike is dissipated afterelapse of a short period of time. An input providing a control signalfor causing the switching off of the switching transistor when thecontrol signal changes from a first value to a second value. The currentclamping circuit (i) opens an additional path for the current from theswitching transistor when the control signal changes from the firstvalue to the second value in order that the parasitic spike is onlypartially communicated through the one of the first and second paths;and (ii) closes the additional path after the additional path has beenopen for the short period of time.

According to another example embodiment, there is a method for clampingcurrent in a charge pump. The charge pump includes switching circuitryand a capacitor, and the charge pump defines first and second paths. Foreach of the first and second paths, a selected one of the followingholds i) current is transmitted to the capacitor; and ii) current isreceived from the capacitor. At least one parasitic spike in currentfrom at least one of a number of transistors of the switching circuitryis generated during switching off of the at least one transistor. Themethod includes the step of providing at least one control signal thatcauses the switching off of the at least one transistor when the atleast one control signal changes from a first value to a second value.The method also includes the step of opening an additional path for thecurrent from the at least one of the transistors when the at least onecontrol signal changes from the first value to the second value in orderthat the at least one parasitic spike is only partially communicatedthrough a selected one of the first and second paths. The additionalpath is provided to the at least one of the transistors through a firstnode. Voltage at the first node changing in value during the switchingoff of the at least one transistor. The method also includes the stepof, after the at least one of the transistors has switched off,minimizing leakage current flow through a transistor on the one of thefirst and second paths, relative to the capacitor.

Conveniently, the step of minimizing the leakage current flow mayinclude preventing voltage at the first node from drifting away from afixed voltage value while the at least one transistor is switched off

Expediently, the method may further include the step of closing theadditional path momentarily after its having been opened.

According to another example embodiment, there is an apparatus includinga charge pump. The charge pump includes a number of switchingtransistors, a current clamping circuit and a capacitor, and the chargepump defines first and second paths. For each of the first and secondpaths, a selected one of the following holds i) current is transmittedto the capacitor; and ii) current is received from the capacitor. One ofthe switching transistors and a first node are located on a selected oneof the first and second paths. The switching transistor generates aparasitic spike in current when it switches off. A circuit is capable ofproviding control signals for causing the switching off of the switchingtransistor when one of the control signals changes from a first value toa second value. The current clamping circuit (i) opens an additionalpath for the current from the switching transistor when the controlsignal changes from the first value to the second value in order thatthe parasitic spike is only partially communicated through the one ofthe first and second paths. The additional path is provided to theswitching transistor through the first node. Voltage at the first nodechanging in value during the switching off of the switching transistor.The current clamping circuit also (ii) after the at least one of thetransistors has switched off, minimizing leakage current flow through atransistor on the one of the first and second paths, relative to thecapacitor.

Conveniently, the minimizing of the leakage current flow may includepreventing voltage at the first node from drifting away from a fixedvoltage value while the at least one transistor is switched off

Expediently, the charge pump may further include first and second FETsboth electrically connected to the capacitor, the first FET positionedalong the first path, the second FET positioned along the second path.

Conveniently, the current clamping circuit may include two transistorsconnected in series and located along the additional path, the currentclamping circuit coupling the first node to a second node between thetwo transistors when the additional path becomes open.

Expediently, the charge pump may further define a Vc node at thecapacitor, and the current clamping circuit may including a repeater forgenerating a replica of voltage at the Vc node, the replicated voltagebeing coupled to the first node once the additional path becomes open.

Accordingly, it would be advantageous to improve circuits for clampingcurrent in a charge pump.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made, by way of example, to the accompanyingdrawings:

FIG. 1 is a circuit schematic representation of a charge pump;

FIG. 2 is an example waveform graph illustrating currents throughparticular paths of the circuit of FIG. 1 over time;

FIG. 3 is a circuit schematic representation of another charge pumpsimilar in certain respects to the charge pump of FIG. 1, butadditionally including a static clamp;

FIG. 4 is a circuit schematic representation of another charge pumpsimilar in certain respects to the charge pump of FIG. 1, butadditionally including a clamp in accordance with an example embodiment;

FIG. 5 is a circuit schematic representation of another charge pump thatincludes a clamp in accordance with a second example embodiment;

FIG. 6 is a circuit schematic representation of another charge pump thatincludes a clamp in accordance with a third example embodiment;

FIG. 7 is a circuit schematic representation of another charge pump thatincludes a clamp in accordance with a fourth example embodiment;

FIG. 8 is a circuit schematic representation of another charge pump thatincludes a clamp in accordance with a fifth example embodiment;

FIG. 9 is a circuit schematic representation of another charge pump thatincludes a clamp in accordance with a sixth example embodiment;

FIG. 10 is a circuit schematic representation of another charge pumpthat includes a clamp in accordance with a seventh example embodiment;

FIG. 11 is a circuit schematic representation of another charge pumpthat includes a clamp in accordance with an eighth embodiment;

FIG. 12 is a circuit schematic representation of another charge pumpthat includes a clamp in accordance with a ninth example embodiment;

FIG. 13 is a circuit schematic representation of another charge pumpthat includes a clamp in accordance with a tenth example embodiment; and

FIG. 14 shows diagrammatic graphs illustrating signals applied to gatesof transistors of the clamp shown in FIG. 4, and another examplewaveform graph also being shown, the waveform graph illustratingcurrents through particular portions of the circuit of FIG. 4 over time;

FIG. 15 is a circuit schematic representation of another charge pumpconceptually similar to the charge pump of FIG. 4, but comprised ofbipolar transistors instead of FETs; and

FIG. 16 is a circuit schematic representation of another charge pumpconceptually similar to the charge pump of FIG. 5, but comprised ofbipolar transistors instead of FETs.

Similar or the same reference numerals may have been used in differentfigures to denote similar components.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of example embodiments, a numberof illustrated circuits and circuit components are of a type whichperforms known operations on electronic signals. Those skilled in theart will have knowledge of alternative circuits or circuit componentswhich are recognized as equivalent because they provide the sameoperations on the signals.

Referring now to the drawings, FIG. 1 is a circuit schematicrepresentation of a charge pump 100. In some examples, the charge pump100 will be a part of a memory circuit (for instance, DRAM) and used ina PLL to control a voltage applied to a VCO. In other examples, thecharge pump 100 may similarly be a part of some memory circuit, but usedin, for instance, a DLL instead of a PLL. In additional examples, thecharge pump 100 may be a part of clock management/distributioncircuitry, a memory interface, an FPGA module, etc.

The charge pump 100 includes a capacitor 102. The charge pump 100 alsoincludes switching circuitry, which in the illustrated example iscomprised of a PMOS switching transistor 104 and an NMOS switchingtransistor 108. The switching transistor 104 is switched in response toa pump-up control signal PU applied at its gate 112. The switchingtransistor 108 is switched in response to a pump-down control signal PDapplied at its gate 116.

With respect to the illustrated charge pump 100, neither the switchingtransistor 104, nor the switching transistor 108 is directly connectedto output node V_(c). Those skilled in the art will have knowledge ofcircuits wherein the switching transistors are directly connected to theoutput node; however, one drawback of such a configuration is theinduction of parasitic noise into the output node at those instances inwhich there is a signal transition at the gates of the switchingtransistors.

In the illustrated example, connected between the two switchingtransistors 104 and 108 are a PMOS transistor 120 and an NMOS transistor124, each having a bias voltage applied to their gate. In some examples,a current mirror will be employed to implement a voltage referencesource that provides the bias voltage. The transistor 120 with aV_(biasp) applied at its gate 128 is in a state permitting current I_(p)to flow through its channel, sourced into node 130 when the switchingtransistor 104 is on as dictated by the signal PU applied at the gate112. As will be appreciated by those skilled in the art, a gate is thecontrol electrode of a FET permitting transition between on and offstates of the FET to be controlled. In other types of transistors, thecontrol electrode is not necessarily termed a gate. For example, in abipolar transistor the term “base” is typically used in reference to thecontrol electrode of the bipolar transistor.

It will be understood that the switching transistor 104 is switched onwhen the signal PU changes from logic “high” to logic “low”. Vice versathe switching transistor 104 is switched off when the signal PU changesfrom logic low to logic high. Conversely, the transistor 124 with aV_(biasn) applied at its gate 132 is in a state permitting current I_(n)to flow through its channel so as to be drained from the node 130 whenthe switching transistor 108 is on as dictated by the signal PD appliedat the gate 116. It will be understood that the switching transistor 108is switched on when the signal PD changes from logic low to logic high.Vice versa the switching transistor 108 is switched off when the signalPD changes from logic high to logic low.

For convenience of reference, it would be accurate to describe thecharge pump 100 as having both a source portion and a sink portion. Thetransistors 112 and 120 are a part of the source portion. Thetransistors 116 and 124 are a part of the sink portion. (Those skilledin the art will appreciate that the “sink portion” may alternatively bereferred to as the “drain portion”.)

FIG. 2 is an example waveform graph illustrating currents I_(p) andI_(n) over time. In the graph of FIG. 2, times t₁, t₂ and t₃ correspondto instances in time during which one or more of the switchingtransistors 104 and 108 are switched on or off. In particular, at abouttime t₁ the switching transistor 108 is switched on, at about time t₂the switching transistor 104 is switched on, and at about time t₃ boththe switching transistors 104 and 108 are switched off

Referring to time t₃, it will be seen that there is an upward spike 204in the current I_(p) as the switching transistor 104 is switched off.Also at time t₃, there is a downward spike 208 in the current I_(n) asthe switching transistor 108 is switched off. An explanation for thecurrent spikes 204 and 208 are as follows. When either the switchingtransistor 104 or 108 is switching off, they generate current as aresult of switching signal coupling caused by gate-to-draincapacitances. This current is added to the current already flowingthrough the transistor. In the charge pump of FIG. 1, this added currenthas nowhere to go except through the respective adjacent transistor 120or 124.

As will be appreciated by those skilled in the art, the current spikes204 and 208 will cause error in the loop of the DLL/PLL resulting in aphase offset. At least one reason for this will be due to the fact thatthe current spike 204 is not symmetrical to the current spike 208. Also,current tail outs 216 and 220 may also cause error in the loop of theDLL/PLL. As will be appreciated by those skilled in the art, the currenttail outs 216 and 220 exist because the transistors 120 and 124 shut offgradually as opposed to quickly (the voltage at the sources of thetransistors 120 and 124 transition to a shut-off voltage value graduallyrather than quickly).

FIG. 3 is a circuit schematic representation of another charge pump 300similar in certain respects to the charge pump of FIG. 1, butadditionally including a static clamp 304 to provide a path foroff-switching current from the switching transistors 104 or 108. Theillustrated static clamp 304 comprises an NMOS transistor 308 and a PMOStransistor 312. Drain 316 of the transistor 308 is electricallyconnected to the switching transistor 104 through node 320. With respectto the transistor 312, its drain 324 is electrically connected to theswitching transistor 108 through node 328.

It will be understood that the static clamp 304 of the charge pump 300acts to abate current spikes along a path between the switchingtransistor 104 and the capacitor 102 during off-switching of theswitching transistor 104 by providing an additional path for current,and likewise along another path between the switching transistor 108 andthe capacitor 102 during off-switching of the switching transistor 108,also by providing an additional path for current. In terms of thedesigned impact that the static clamp 304 would have on the waveformsshown in FIG. 2, the current spikes would be significantly smaller insize as compared to the illustrated current spikes 204 and 208. Also,the current tail outs would be reduced.

A limitation of the static clamp 304 when used within the charge pump300 is that V_(c) is constricted to a range having an upper limitdefined by V_(biasp) and a lower limit defined by V_(biasn). As will beappreciated by one skilled in the art, this V_(c) limitation is causedby the transistors 308 and 312 remaining turned on even after theswitching transistors 104 and 108 have switched off. In particular, thevoltage at the node 320 will approach ground potential once theswitching transistor 104 has been switched off. If V_(c) is broughtabove V_(biasp), current will flow through the transistor 120 in adirection opposite the direction shown by the arrow for current I_(p″)(the higher the voltage value to which V_(c) is brought, the greater theleakage current) and current I_(p″) will have an undesirable effect onthe value of V_(c). Similarly, the voltage at the node 328 will approachV_(dd) once the switching transistor 108 has been switched off. If V_(c)is brought below V_(biasn), current will flow through the transistor 124in a direction opposite the direction shown by the arrow for currentI_(n″) (in this case the lower the voltage value to which V_(c) isbrought, the greater the leakage current) and so to will current I_(n″)have an undesirable effect on the value of V_(c).

Reference will now be made to FIG. 4. FIG. 4 is a circuit schematicrepresentation of another charge pump 500 similar in certain respects tothe charge pump of FIG. 1, but additionally including a clamp 504 inaccordance with an example embodiment. Like the static clamp 304 (FIG.3) the clamp 504 can provide an additional path for off-switchingcurrent from either of the switching transistors 104 or 108; howeverunlike the static clamp 304, the clamp 504 does not force V_(c) to beconstricted to a range within the limits defined by V_(biasp) andV_(biasn).

The illustrated clamp 504 comprises a pair of NMOS transistors 508 and512, a pair of PMOS transistors 516 and 520, a delay introducinginverter circuitry (or inverter) 524, and another delay introducinginverter circuitry 528. (Each of the inverters 524 and 528 can beimplemented using a well known combination of transistors such as anNMOS-PMOS transistor pair, for example. Also, although the delayintroducing inverter circuitry 524 and the delay introducing invertercircuitry 528 are each shown as only a single inverter in FIG. 4, itwill be understood that in some examples the delay introducing invertercircuitry can comprise three or more actual inverters as opposed to asingle inverter.)

It will be understood that optimal delay introducible by invertercircuitry in clamps according to example embodiments will vary dependingupon a variety of factors. These factors can include, for example, thesize of the transistors that are providing the additional path forcurrent and the size of the transistors used to implement the invertercircuitry.

In the illustrated example embodiment, half of the clamp 504, comprisingthe transistor 508, the transistor 512 and the inverter 524, is inoperative communication with the switching transistor 104, and the otherhalf of the clamp 504, comprising the transistor 516, the transistor 520and the inverter 528, is in operative communication with the switchingtransistor 108.

With respect to the half of illustrated clamp 504 that is in operativecommunication with the switching transistor 104, drain 532 of thetransistor 508 is electrically connected to the switching transistor 104through node 536. Also, source 540 of the transistor 508 is electricallyconnected to drain 544 of the transistor 512. Both input 548 of theinverter 524 and gate 552 of the transistor 508 are applied with thesame signal, namely PU. Output 556 of the inverter 524 is electricallyconnected to gate 560 of the transistor 512.

With respect to the half of illustrated clamp 504 that is in operativecommunication with the switching transistor 108, drain 564 of thetransistor 520 is electrically connected to the switching transistor 108through node 568. Also, source 572 of the transistor 520 is electricallyconnected to drain 576 of the transistor 516. Both input 580 of theinverter 528 and gate 584 of the transistor 520 are applied with thesame signal, namely PD. Output 588 of the inverter 528 is electricallyconnected to gate 592 of the transistor 516.

During simultaneous off-switching of the switching transistors 104 and108 (of course it will be understood that in at least some examples thetwo transistors need not be switched off at the same time) the operationof the illustrated clamp 504 will be as follows. For a brief period oftime, the duration of which will be determined by the delay of theinverters 524 and 528, two transistor pairs forming a part of the clamp504 will provide paths for abating current spikes during off-switchingof the switching transistors 104 and 108. These paths will exist becauseboth transistors of each pair will be turned on. However, after elapseof the inverter delay-determined period of time, neither transistor pairwill have both transistors turned on so the clamping effect of thetransistors pairs will be removed, leaving a greater flexibility forV_(c) to be set as desired (i.e. not constricted to a range within thelimits defined by V_(biasp) and V_(biasn)).

Reference will now be made to FIG. 5. FIG. 5 is a circuit schematicrepresentation of another charge pump 600 similar in certain respects tothe charge pump of FIG. 4, but including a clamp 604 in accordance withan alternative example embodiment. Like other clamps illustrated anddescribed herein, the clamp 604 does not force V_(c) to be constrictedto a range within the limits defined by V_(biasp) and V_(biasn).

The illustrated clamp 604 comprises a first pair of transistors 606 and608, and a second pair of transistors 610 and 612. In at least oneexample, the transistors 606 and 610 are NMOS transistors, and thetransistors 608 and 612 are PMOS transistors.

In the illustrated example embodiment, half of the clamp 604, comprisingthe transistors 606 and 608 are in operative communication with theswitching transistor 104, and the other half of the clamp 604,comprising the transistors 610 and 612 are in operative communicationwith the switching transistor 108.

With respect to the half of illustrated clamp 604 that is in operativecommunication with the switching transistor 104, drain 614 of thetransistor 606 is electrically connected to the switching transistor 104through node 616. Also, source 618 of the transistor 606 is electricallyconnected to source 620 of the transistor 608. Both gate 622 of thetransistor 606 and gate 624 of the transistor 608 are applied with thesame signal, namely PU.

With respect to the half of illustrated clamp 604 that is in operativecommunication with the switching transistor 108, drain 626 of thetransistor 612 is electrically connected to the switching transistor 108through node 628. Also, source 630 of the transistor 612 is electricallyconnected to source 632 of the transistor 610. Both gate 634 of thetransistor 612 and gate 636 of the transistor 610 are applied with thesame signal, namely PD.

When the signal PD is logic high, the transistors 108 and 610 will beconducting, whereas the transistor 612 will not be conducting. Duringthis time, the node between the sources 630 and 632 is pre-charged to avoltage level roughly equal to the threshold voltage level of the NMOStransistor 610. When the signal PD goes logic low, the transistor 610turns off cutting off the leakage path. Also, the PMOS transistor 612turns on providing for charge exchange between the node 628 and the nodebetween the sources 630 and 632. For example, charge exchange occursbetween the parasitic capacitances of the two transistors 610 and 612.During this time of charge exchange, an additional current path throughthe node 628 is provided, in order that the parasitic current spike willonly partially travel through the path between the switching transistor108 and the capacitor 102. As a result of the charge exchange, thevoltage level of the node 628 is driven sharply up making the transistor124 cut off sharply. The new voltage value to which voltage at the node628 transitions is maintained while the switching transistor 108 isswitched off, in order that leakage current flow is minimized duringthis passive phase.

Similarly, when the signal PU is logic low, the transistors 104 and 608will be conducting, and the transistor 606 will not be conducting. Whenthe signal PU goes logic high, the transistor 608 will turn off cuttingoff leakage path. Also, the transistor 606 turns on providing for chargeexchange between the node 616 and the node between the two sources 618and 620. For example, charge exchange occurs between parasiticcapacitances of the transistors 606 and 608. During this time of chargeexchange, an additional current path through the node 616 is provided,in order that the parasitic current spike will only partially travelthrough the path between the switching transistor 104 and the capacitor102. As a result of the charge exchange, the voltage level of the node616 is driven sharply down making the transistor 120 cut off sharply.The new voltage value to which voltage at the node 616 transitions ismaintained while the switching transistor 104 is switched off, in orderthat leakage current flow is minimized during this passive phase.

Reference will now be made to FIG. 6. FIG. 6 is a circuit schematicrepresentation of another charge pump 650, again similar in certainrespects to the charge pump of FIG. 4, but including a clamp 654 inaccordance with an another alternative example embodiment. Like otherclamps illustrated and described herein, the clamp 654 does not forceV_(c) to be constricted to a range within the limits defined byV_(biasp) and V_(biasn).

The illustrated clamp 654 comprises an NMOS transistor 656 having thesignal PU applied at its gate 657, a PMOS transistor 658 having thesignal PD applied at its gate 659, and an analogue repeater 660. Input662 of the repeater 660 is connected to the node 130, whereas output 664of the repeater 660 is electrically connected to source 666 of thetransistor 656 and source 668 of the transistor 658.

Within the illustrated clamp 654, the transistor 656 is in operativecommunication with the switching transistor 104. In particular, drain670 of the transistor 656 is electrically connected to the switchingtransistor 104 through node 672. Additionally, the transistor 658 is inoperative communication with the switching transistor 108. Inparticular, drain 674 of the transistor 658 is electrically connected tothe switching transistor 108 through node 676.

As will be appreciated by those skilled in the art, the transistor 656will start conducting during off-switching as a result of a logic highsignal applied to the gate 657. Thus, with the transistor 656conducting, a replica of the V_(c) voltage provided by the repeater 660is coupled to the node 672. Leakage current is minimized because thevoltage drop across the leakage current path is small and the voltage atthe node 672 is prevented from significantly falling in value while thetransistor 104 is switched off. Also, the off-switching generated,parasitic current spike will only partially travel through the pathbetween the switching transistor 104 and the capacitor 102 (again anadditional current path through the node 672 is provided when thetransistor 656 is conducting).

Similarly, during off-switching of the transistor 108 the transistor 658will start conducting because of a logic high signal applied at the gate659. Because the transistor 658 is conducting, a replica of the V_(c)voltage provided by the repeater 660 is coupled to the node 676. Again,leakage current is minimized because the voltage difference across theleakage current path is small and a voltage at the node 676 is preventedfrom rising by any significant amount while the transistor 108 isswitched off. Furthermore, it will again be understood that theoff-switching generated, parasitic current spike (sink portion ofcircuit) will only partially travel through the path between theswitching transistor 108 and the capacitor 102 (again an additionalcurrent path through the node 676 is provided when the transistor 658 isconducting).

In some examples, the repeater 660 will be absent. For instance, thenodes 672 and 676 might be coupled directly to the node 130 duringphases when the transistors 104 and 108 are switched off. There willhowever be some commutation charge injection in such instances. Inparticular, parasitic capacitances of the transistors 656 and 658 cancause commutation charge injections into the node 130.

Reference will now be made to FIG. 7. FIG. 7 is a circuit schematicrepresentation of another charge pump 700 that includes a clamp 704 inaccordance with yet another alternative example embodiment. It will beseen that the charge pump 700 is similar in certain respects to othercharge pumps previously illustrated and described. For example, like anumber of other clamps illustrated and described herein, the clamp 704does not force V_(c) to be constricted to a range within the limitsdefined by V_(biasp) and V_(biasn).

The illustrated clamp 704 comprises two inverters 706 and 708, a PMOStransistor 710, an NMOS transistor 712 and an analogue repeater 714. Interms of circuit configuration, input 716 of the inverter 706 receivesthe signal PU and output 718 of the inverter 706 is applied to gate 720of the transistor 710. Likewise, input 724 of the inverter 708 receivesthe signal PD and output 728 of the inverter 708 is applied to gate 732of the transistor 712. Also, input 736 of the repeater 714 is connectedto the node 130, whereas output 740 of the repeater 714 is electricallyconnected to drain 744 of the transistor 710 and drain 748 of thetransistor 712.

Within the illustrated clamp 704, the transistor 710 is in operativecommunication with the switching transistor 104. In particular, drain752 of the transistor 710 is electrically connected to the switchingtransistor 104 through node 756. Additionally, the transistor 712 is inoperative communication with the switching transistor 108. Inparticular, drain 760 of the transistor 712 is electrically connected tothe switching transistor 108 through node 764.

It will be understood that the clamp 704 of FIG. 7 is similar inoperation to the clamp 654 of FIG. 6. Again, the illustrated repeaterwill not be present in all examples.

Reference will now be made to FIG. 8. FIG. 8 is a circuit schematicrepresentation of another charge pump 800 that includes a clamp 804 inaccordance with yet another alternative example embodiment. Once again,it will be seen that the charge pump 800 is similar in certain respectsto other charge pumps previously illustrated and described. For example,like a number of other clamps illustrated and described herein, theclamp 804 does not force V_(c) to be constricted to a range within thelimits defined by V_(biasp) and V_(biasn).

The illustrated clamp 804 comprises a pair of PMOS transistors 808 and812, a pair of NMOS transistors 816 and 820, and two inverters 824 and828. Half of the clamp 804, comprising the transistor 808, thetransistor 812 and the inverter 824, is in operative communication withthe switching transistor 104, and the other half of the clamp 804,comprising the transistor 816, the transistor 820 and the inverter 828,is in operative communication with the switching transistor 108.

With respect to the half of illustrated clamp 804 that is in operativecommunication with the switching transistor 104, source 832 of thetransistor 808 is electrically connected to the switching transistor 104through node 836. Also, drain 840 of the transistor 808 is electricallyconnected to source 844 of the transistor 812, and the voltage at thenode between the drain 840 and the source 844 will not drop to groundpotential. Input 848 of the inverter 824 and the gate 112 of thetransistor 104 are applied with the same signal, namely PU. Output 856of the inverter 824 is electrically connected to gate 860 of thetransistor 808. A signal V_(biasp1) is applied to gate 862 of thetransistor 812. (In at least some examples, V_(biasp1) will have asimilar, or essentially the same value as V_(biasp)).

With respect to the half of illustrated clamp 804 that is in operativecommunication with the switching transistor 108, source 864 of thetransistor 820 is electrically connected to the switching transistor 108through node 868. Also, drain 872 of the transistor 820 is electricallyconnected to source 876 of the transistor 816, and the voltage at thenode between the drain 872 and the source 876 will not rise to V_(dd).Input 880 of the inverter 828 and the gate 116 of the transistor 108 areapplied with the same signal, namely PD. Output 882 of the inverter 828is electrically connected to gate 884 of the transistor 820. A signalV_(biasn1) is applied to gate 894 of the transistor 816. (In at leastsome examples, V_(biasn), will have a similar, or essentially the samevalue as V_(biasn).)

Still with reference to the half of illustrated clamp 804 that is inoperative communication with the switching transistor 108, it will beunderstood that during off-switching of transistor 108 the transistor820 will start conducting, thus providing for the exchange of chargebetween the node 868 and the node between the drain 872 and the source876 (for example, parasitic capacitances of the transistors 816 and 820will exchange charge with each other). By appropriate selection of thesize of the transistor 816 and the value of V_(biasn1), the voltagelevel at the node 868 can be caused to rise when the transistor 108 isswitched off, thus producing a sharp cut-off of tail out current. Inparticular, the immediate voltage transition will be roughly fromV_(biasn)-V_(T) _(—) _(n) to V_(biasn1)-V_(T) _(—) _(n1). Also, theclamp 804 will restrict the voltage at the node 868 from falling belowV_(biasn1)-V_(T) _(—) _(n1), and because only miniscule leakage currentwill exist as long as the voltage at the node 868 does not fall belowV_(biasn)-VT _(—) _(n), the clamp 804 will effectively maintain thevoltage at the node 868 close to V_(biasn1)-VT _(—) _(n1) while theswitching transistor 108 is switched off.

With reference to the half of illustrated clamp 804 that is in operativecommunication with the switching transistor 104, it will be understoodthat when the transistor 104 is switching off, the transistor 808 willstart conducting, thus providing for the exchange of charge between thenode 836 and the node between the drain 840 and the source 844 (forexample, the parasitic capacitances of the transistors 808 and 812 willexchange charge with each other). By appropriate selection of the sizeof the transistor 812 and the value of V_(biasp1), a large enough dropin the voltage level at the node 836 will occur when the transistor 104is switched off so as to produce a sharp cut-off of tail out current. Inparticular, the immediate voltage transition will be roughly fromV_(biasp)+V_(T) _(—) _(p) to V_(biasp1)+V_(T) _(—) _(p1). Also, theclamp 804 will restrict the voltage at the node 836 from rising aboveV_(biasp1)+V_(T) _(—) _(p1), and because only miniscule leakage currentwill exist as long as the voltage at the node 836 does rise aboveV_(biasp)+V_(T) _(—) _(p), the clamp 804 will effectively maintain thevoltage at the node 836 close to V_(biasp1)+V_(T) _(—) _(p1) while theswitching transistor 104 is switched off.

An additional note in relation to the example embodiment illustrated inFIG. 8: a leakage current path does exist when either of the switchingtransistors is switched off. In particular, the leakage current pathsare i) the path through the transistors 120, 808 and 812; and ii) thepath through the transistors 124, 820 and 816; however, leakage currentwill be small as compared to, for example, the charge pump 300 shown inFIG. 3. Also, the clamp 804 may optionally include very small currentsources 896 and 898 to further ensure maintenance of the voltage at thenodes 836 and 868 close to a constant value while the switchingtransistors are switched off. These current sources will counteractequally small currents caused by parasitic capacitances. In one example,the current source 896 is implemented using a PMOS transistor (with thesource and gate of the PMOS transistor connected to V_(dd) and V_(biasp)respectively) and the current source 898 is implemented using an NMOStransistor (with the source and gate of the NMOS transistor connected toground potential and V_(biasn) respectively).

Reference will now be made to FIG. 9. FIG. 9 is a circuit schematicrepresentation of another charge pump 900 that includes a clamp 904 inaccordance with yet another alternative example embodiment. Once again,it will be seen that the charge pump 900 is similar in certain respectsto other charge pumps previously illustrated and described. For example,like a number of other clamps illustrated and described herein, theclamp 904 does not force V_(c) to be constricted to a range within thelimits defined by V_(biasp) and V_(biasn).

The illustrated clamp 904 comprises a PMOS transistor 908, an NMOStransistor 920, and two inverters 924 and 928. Half of the clamp 904,comprising the transistor 908 and the inverter 924, is in operativecommunication with the switching transistor 104, and the other half ofthe clamp 904, comprising the transistor 920 and the inverter 928, is inoperative communication with the switching transistor 108.

With respect to the half of illustrated clamp 904 that is in operativecommunication with the switching transistor 104, source 932 of thetransistor 908 is electrically connected to the switching transistor 104through node 936. Also, the signal V_(biasp) is applied to drain 940 ofthe transistor 908. Input 948 of the inverter 924 and the gate 112 ofthe transistor 104 are applied with the same signal, namely PU. Output956 of the inverter 924 is electrically connected to gate 960 of thetransistor 908.

With respect to the half of illustrated clamp 904 that is in operativecommunication with the switching transistor 108, source 964 of thetransistor 920 is electrically connected to the switching transistor 108through node 968. Also, the signal V_(biasn) is applied to drain 972 ofthe transistor 920. Input 980 of the inverter 928 and the gate 116 ofthe transistor 108 are applied with the same signal, namely PD. Output982 of the inverter 928 is electrically connected to gate 984 of thetransistor 920.

The operation of the clamp 904 is similar to the operation of the clamp804 shown in FIG. 8. The primary difference between the two clamps isthat the clamp 904 lacks the transistors 812, 816, and the correspondingbiasing voltages applied to their gates. Instead, the drain 940 of thetransistor 908 is coupled to V_(biasp), and similarly the drain 972 ofthe transistor 920 is coupled to V_(biasn).

Reference will now be made to FIG. 10. FIG. 10 is a circuit schematicrepresentation of another charge pump 1000 that includes a clamp 1004,in accordance with yet another alternative example embodiment, and whichcomprises an NMOS transistor 1008 and a PMOS transistor 1012. Onceagain, it will be seen that the charge pump 1000 is similar in certainrespects to other charge pumps previously illustrated and described. Forexample, like a number of other clamps illustrated and described herein,the clamp 1004 does not force V_(c) to be constricted to a range withinthe limits defined by V_(biasp) and V_(biasn). Also, it will beunderstood that the clamp 1004 is particularly similar to the clamp 904shown in FIG. 9, the primary difference between the two clamps beingthat the inverters have been eliminated by replacing the PMOS transistor908 with an NMOS transistor, and by replacing the NMOS transistor 920with a PMOS transistor.

With respect to the NMOS transistor 1008, this transistor is inoperative communication with the switching transistor 104. Inparticular, drain 1016 of the transistor 1008 is electrically connectedto the switching transistor 104 through node 1020. Also, the signalV_(biasp) is applied to drain 1024 of the transistor 1008. Gate 1028 ofthe transistor 1008 and the gate 112 of the transistor 104 are appliedwith the same signal, namely PU.

With respect to the PMOS transistor 1012, this transistor is inoperative communication with the switching transistor 108. Drain 1032 ofthe transistor 1012 is electrically connected to the switchingtransistor 108 through node 1036. Also, the signal V_(biasn) is appliedto source 1040 of the transistor 1012. Gate 1044 of the transistor 1012and the gate 116 of the transistor 108 are applied with the same signal,namely PD.

For some applications, effectiveness of the clamp 1004 may be improvedby use of larger transistors (i.e. increasing the size of the transistor1008 and/or the transistor 1012).

Reference will now be made to FIG. 11. FIG. 11 is a circuit schematicrepresentation of another charge pump 1100 that includes a clamp 1104 inaccordance with yet another alternative example embodiment. Once again,it will be seen that the charge pump 1100 is similar in certain respectsto other charge pumps previously illustrated and described. For example,like a number of other clamps illustrated and described herein, theclamp 1104 does not force V_(c) to be constricted to a range within thelimits defined by V_(biasp) and V_(biasn).

The illustrated clamp 1104 comprises a pair of NMOS transistors 1108 and1112, a pair of PMOS transistors 1116 and 1120, a delay introducinginverter circuitry (or inverter) 1124, another delay introducinginverter circuitry 1128, and two additional transistors 1132 and 1136.

In the illustrated example embodiment, half of the clamp 1104,comprising the transistors 1108, 1112, 1132 and the inverter 1124, is inoperative communication with the switching transistor 104, and the otherhalf of the clamp 1104, comprising the transistors 1116, 1120, 1136 andthe inverter 1128, is in operative communication with the switchingtransistor 108.

With respect to the half of illustrated clamp 1104 that is in operativecommunication with the switching transistor 104, drain 1140 of thetransistor 1108 is electrically connected to the switching transistor104 through node 1144. Also, source 1148 of the transistor 1108 iselectrically connected to drain 1152 of the transistor 1112, as well asto gate 1156 of the transistor 1132. Both input 1160 of the inverter1124 and gate 1164 of the transistor 1108 are applied with the samesignal, namely PU. Output 1168 of the inverter 1124 is electricallyconnected to both source 1172 and drain 1176 of the transistor 1132, aswell as to gate 1180 of the transistor 1112.

With respect to the half of illustrated clamp 1104 that is in operativecommunication with the switching transistor 108, drain 1181 of thetransistor 1120 is electrically connected to the switching transistor108 through node 1182. Also, source 1184 of the transistor 1120 iselectrically connected to drain 1185 of the transistor 1116. Both input1187 of the inverter 1128 and gate 1188 of the transistor 1120 areapplied with the same signal, namely PD. Output 1190 of the inverter1128 is electrically connected to both drain 1192 and source 1194 of thetransistor 1136, as well as to gate 1196 of the transistor 1116.

The operation of the clamp 1104 is similar to the operation of the clamp504 shown in FIG. 4; however, the clamp 1104 includes additionaltransistors 1132 and 1136 configured as capacitor-plugged devices. Thetransistor 1132 functions as a capacitor and acts to pump additionalcharge into the node 1144 during off-switching of the transistor 104.The transistor 1136 also acts as a capacitor, and functions to sinkadditional charge from the node 1182 during off-switching of thetransistor 108. It will be understood that the transistors 1132 and 1136need not be non-standard as the voltage drop across their plates shouldnot get smaller than the threshold voltage of the transistor.

Reference will now be made to FIG. 12. FIG. 12 is a circuit schematicrepresentation of another charge pump 1200 that includes a clamp 1204 inaccordance with yet another alternative example embodiment. It will beseen that the charge pump 1200 is similar in certain respects to othercharge pumps previously illustrated and described. For example, like anumber of other clamps illustrated and described herein, the clamp 1204does not force V_(c) to be constricted to a range within the limitsdefined by V_(biasp) and V_(biasn).

The illustrated clamp 1204 comprises two inverters 1208 and 1212, twotransmission gates 1216 and 1220, and an analogue repeater 1224. Interms of circuit configuration, the signal PU is received by bothcontrol input 1227 of the transmission gate 1216 and input 1228 of theinverter 1208 and output 1232 of the inverter 1208 is applied to controlinput 1236 of the transmission gate 1216. Likewise, the signal PD isreceived by both control input 1239 of the transmission gate 1220 andinput 1240 of the inverter 1212, and output 1244 of the inverter 1212 isapplied to control input 1248 of the transmission gate 1220. Also, input1252 of the repeater 1224 is connected to the node 130, whereas output1256 of the repeater 1224 is electrically connected to inputs 1260 and1264 of the transmission gates 1216 and 1220 respectively.

Within the illustrated clamp 1204, the transmission gate 1216 is inoperative communication with the switching transistor 104. Inparticular, output 1270 of the transmission gate 1216 is electricallyconnected to the switching transistor 104 through node 1272.Additionally, the transmission gate 1220 is in operative communicationwith the switching transistor 108. In particular, output 1272 of thetransmission gate 1220 is electrically connected to the switchingtransistor 108 through node 1285.

During off-switching of the transistor 104, the transmission gate 1216starts conducting, and thus the node 1272 will be coupled to the node atthe output 1256 of the repeater 1224 (V_(cs) node). Leakage current isminimized because the voltage drop across the leakage current path issmall and the voltage at the node 1272 is prevented from significantlyfalling in value while the transistor 104 is switched off. Also, theoff-switching generated, parasitic current spike will only partiallytravel through the path between the switching transistor 104 and thecapacitor 102 (an additional current path through the node 1272 isprovided when the transmission gate 1216 is conducting).

Similarly, during off-switching of the transistor 108, the transmissiongate 1220 starts conducting causing the node 1285 to be coupled to theV_(cs) node. Because replica voltage V_(cs) will be very close tovoltage V_(c) which is being replicated, the node 1285 (or alternativelythe node 1272) is coupled to a node having a voltage value close toV_(c) when the switching transistor is switched off. Thus, the voltagedrop across the leakage path will be small enough for leakage to beminimized. Again, the off-switching generated, parasitic current spike(source portion of circuit) will only partially travel through the pathbetween the switching transistor 108 and the capacitor 102 (anadditional current path through the node 1285 is provided when thetransmission gate 1220 is conducting).

Reference will now be made to FIG. 13. FIG. 13 is a circuit schematicrepresentation of another charge pump 1300 that includes a clamp 1304 inaccordance with yet another alternative example embodiment. It will beseen that the charge pump 1300 is similar in certain respects to othercharge pumps previously illustrated and described. For example, like anumber of other clamps illustrated and described herein, the clamp 1304does not force V_(c) to be constricted to a range within the limitsdefined by V_(biasp) and V_(biasn).

The illustrated clamp 1304 comprises two inverters 1308 and 1312, twotransmission gates 1316 and 1320, and two transistors 1324 and 1328. Interms of circuit configuration, the signal PU is received by bothcontrol input 1330 of the transmission gate 1316 and input 1332 of theinverter 1308, and output 1334 of the inverter 1308 is applied tocontrol input 1336 of the transmission gate 1316. Likewise, the signalPD is received by both control input 1340 of the transmission gate 1320and input 1342 of the inverter 1312, and output 1344 of the inverter1312 is applied to control input 1346 of the transmission gate 1320.

Within the illustrated clamp 1304, the transmission gate 1316 is inoperative communication with the switching transistor 104. Inparticular, output 1349 of the transmission gate 1316 is electricallyconnected to the switching transistor 104 through node 1350, and an openpath between the node 1350 and ground exists when the NMOS transistor1324 is on and the transistor gate 1316 is conducting. Additionally, thetransmission gate 1320 is in operative communication with the switchingtransistor 108. In particular, output 1352 of the transmission gate 1320is electrically connected to the switching transistor 108 through node1354, and an open path between the node 1354 and V_(dd) exists when thePMOS transistor 1328 is turned on and the transmission gate 1320 isconducting.

During off-switching of the transistor 104, the transmission gate 1316starts conducting, and thus the node 1350 will be coupled to node 1380located between input 1382 of the transmission gate 1316 and drain 1384of the transistor 1324. At the time of off-switching, the node 1380 willbe at about ground potential, and charge exchange between the nodes 1380and 1350 will occur during which voltage at the node 1350 will drop offsharply cutting off tail out current, and also during this time ofcharge exchange, an additional current path through the node 1350 isprovided, in order that the parasitic current spike will only partiallytravel through the path between the switching transistor 104 and thecapacitor 102. The new voltage value to which voltage at the node 1350transitions is maintained while the switching transistor 104 is switchedoff, in order that leakage current flow is minimized during this passivephase. Also, the transistor 1324 will be turned off so that the leakagepath will be broken.

Similarly, during off-switching of the transistor 108, the transmissiongate 1320 starts conducting, and thus the node 1354 will be coupled tonode 1390 located between input 1392 of the transmission gate 1320 anddrain 1394 of the transistor 1328. At the time of off-switching, thenode 1390 will be at about V_(dd), and charge exchange between the nodes1390 and 1354 will occur during which voltage at the node 1354 will risesharply cutting off tail out current, and also during this time ofcharge exchange, an additional current path through the node 1354 isprovided, in order that the parasitic current spike will only partiallytravel through the path between the switching transistor 108 and thecapacitor 102. The new voltage value to which voltage at the node 1354transitions is maintained while the switching transistor 108 is switchedoff, in order that leakage current flow is minimized during this passivephase. Also, the transistor 1328 will be turned off so that the leakagepath will be broken.

Reference will now be made to FIG. 14. Like FIG. 2, an example waveformgraph of currents (over time) is shown in FIG. 14; however for currentsthrough circuit paths shown in FIG. 4 (as opposed to circuit paths shownin FIG. 1). Example signals PU and PD (and derived signals at the gates560 and 592) are also shown in diagrammatic graphs above the examplewaveform graph.

With reference now to FIGS. 4 and 14, it will be observed for a periodof time beginning at time t_(c1) (corresponding to the start ofoff-switching of the transistor 108) and ending at time t_(c2), a valueof logic low (which produces the on state when applied to the gate of aPMOS transistor) will be applied to both the gates of the transistors516 and 520. Thus, for a brief period of time, the pair of transistors516 and 520 will provide an additional path for off-switching currentfrom the transistor 108; however, it will be understood that at othertimes at least one of the transistors 516 and 520 will be turned off,and therefore the additional path will not be provided at such times.With respect to the source portion transistor pair of the clamp 504(i.e. the transistors 508 and 512) they work in a similar manner;however, as will be appreciated by those skilled in the art, it is avalue of logic high (rather than logic low) that produces the on statewhen applied to the gate of an NMOS transistor.

Comparing now plots of current I_(p) and I_(n) in FIG. 2 to plots ofcurrent I_(p′) and I_(n′) in FIG. 14, the effects of the clamp 504 areevident. In particular, it will be seen that there is only asignificantly smaller upward spike 694 in the current I_(p′) as theswitching transistor 104 is switched off. Likewise, there is only asignificantly smaller downward spike 696 at time t_(c2) as the switchingtransistor 108 is switched off. It also evident from the waveform graphthat the clamp 504 effects a sharp cut off of tail out currents, as thecurrents I_(p′) and I_(n′) quickly fall to about 0 μA after time t_(c1).Simulation results for the clamps shown in FIGS. 5 to 13 are similar(significantly smaller current spikes, sharp cut off of tail outcurrents).

Although the charge pumps shown in the accompanying drawings have both asource portion and a sink portion, it will be understood that, in someexamples, a charge pump may only have a source portion or a sinkportion. Also, although the transistors within the circuits of theillustrated example embodiments are FETs, it will be understood that theteachings contained herein provide instruction for the implementation ofcharge pumps with clamps comprised of other types of transistors, suchas bipolar transistors, for example. Referring to FIGS. 15 and 16, thereare circuit schematic representations of example charge pumps 1500 and1600 that includes clamps 1504 and 1604 respectively. The charge pumps1500 and 1600 are conceptually similar to the charge pumps of FIGS. 4and 5 respectively, but are comprised of bipolar transistors instead ofFETs.

Certain adaptations and modifications of the described embodiments canbe made. Therefore, the above discussed embodiments are considered to beillustrative and not restrictive.

The teachings of all patents, published applications and referencescited herein are incorporated by reference in their entirety.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A charge pump comprising: a) a capacitor; a firstinput to connect to a first power supply; a second input to connect to asecond power supply having a voltage lower than the first power supply,a two output phase detector; a first bias input to connect to a firstbias voltage; and a second bias input to connect to a second biasvoltage; and, b) a pump up current path comprising a first transistorconnected between said first input and a first intermediate node thegate connected to the first output of said phase detector, and a secondtransistor connected between the first intermediate node and saidcapacitor the gate connected to said first bias input; and, c) a pumpdown current path comprising a third transistor connected between saidsecond input and a second intermediate node the gate connected to thesecond output of said phase detector, and a fourth transistor connectedbetween the second intermediate node and the capacitor the gateconnected to said second bias input; and, d) a first alternate currentpath connected between the first intermediate node and said second inputconfigured to conduct current for a brief period of time when said firsttransistor is switched to an off state; and, e) a second alternatecurrent path connected between the second intermediate node and saidfirst input configured to conduct current for a brief period of timewhen said third transistor is switched to an off state.
 2. A charge pumpas in claim 1, wherein said first alternate current path furthercomprises a fifth transistor connected to the first intermediate nodeand a third intermediate node; and, a sixth transistor connected to thethird intermediate node and the second input; and, said second alternatecurrent path further comprises a seventh transistor connected to thefirst intermediate node and a fourth intermediate node; and, an eighthtransistor connected to the fourth intermediate node and said firstinput.
 3. A charge pump as in claim 2, wherein said fifth and sixthtransistors are directly connected to the third intermediate node andsaid seventh and eighth transistors are directly connected to the fourthintermediate node.
 4. A charge pump as in claim 2, wherein said firstalternate current path further comprises a first inverter having aninput connected to the first output of the phase detector and a secondinverter connected to the second output of said phase detector, and saidfifth transistor's gate is connected to the first output of said phasedetector, said sixth transistor's gate is connected to the output ofsaid first inverter, and, said seventh transistors gate is connected tothe second output of said phase detector, and said eighth transistor'sgate is connected to the output of said second inverter.
 5. A chargepump as in claim 4, wherein said first, second, seventh, and eighthtransistors have a first polarity and said third, fourth, fifth, andsixth transistors have a second polarity opposite the first polarity. 6.A charge pump as in claim 5 wherein said first, second, seventh, andeighth transistors are PMOS transistors and said third, fourth, fifth,and sixth transistors are NMOS transistors.
 7. A charge pump as claim 4,further comprising a first clamp capacitor connected between the outputof said first inverter and the third intermediate node, and a secondclamp capacitor connected between the output said second inverter andthe fourth intermediate node.
 8. A charge pump as in claim 7, whereinsaid first and second clamp capacitors comprise transistors.
 9. A chargepump as in claim 2, wherein said fifth and sixth transistors each havegates connected to the first output of said phase detector and saidseventh and eighth transistors each have gates connected to the secondoutput of said phase detector.
 10. A charge pump as in claim 9, whereinsaid third, fourth, fifth and eighth transistors have a first polarityand said first, second, sixth and seventh transistors have a secondpolarity opposite the first polarity.
 11. A charge pump as in claim 10,wherein said first, second, sixth, and seventh transistors are PMOStransistors and said third, fourth, fifth, and eighth transistors areNMOS transistors.
 12. A charge pump comprising: a) a capacitor; a firstpower input to connect to a first power supply; a second power input toconnect to a second power supply having a voltage lower than the firstpower supply, a two output phase detector; a first bias input to connectto a first bias voltage; and a second bias input to connect to a secondbias voltage; a first voltage source having a voltage between the firstpower supply voltage and the second power supply voltage; a secondvoltage source having a voltage between the first power supply voltageand the second power supply voltage; and, b) a pump up current pathcomprising a first transistor connected between said first power inputand a first intermediate node the gate connected to the first output ofsaid phase detector; and, a second transistor connected between thefirst intermediate node and said capacitor the gate connected to saidfirst bias input; and, c) a pump down current path comprising a thirdtransistor connected between said second power input and a secondintermediate node the gate connected to by a second output of said phasedetector; and, a fourth transistor connected between the secondintermediate node and said capacitor the gate connected to said secondbias input; and, d) a first switch connected between the firstintermediate node and said first voltage source configured to turn onwhen said first transistor is turned off; and, e) a second switchconnected between the second intermediate node and said second voltagesource configured to turn on when said third transistor is turned off.13. A charge pump as in claim 12, wherein the said first voltage sourceand said second voltage source are a common voltage source.
 14. A chargepump as in claim 13, wherein said common voltage source is provided by arepeater which replicates the voltage on said capacitor.
 15. A chargepump as in claim 12, wherein said first switch comprises a fifthtransistor and said second switch comprises a sixth transistor.
 16. Acharge pump as in claim 15, wherein the gate of the fifth transistor isconnected to the first output of the phase detector and the gate of thesixth transistor is connected to the second output of the phasedetector.
 17. A charge pump as in claim 15, further comprising a firstinverter having an input connected to the first output of the phasedetector and a second inverter having an input connected to the secondoutput of the phase detector, wherein the gate of the fifth transistoris connected to the output of the first inverter and the gate of thesixth transistor is connected to the output of the second inverter. 18.A charge pump as in claim 12, wherein said first voltage source is thefirst bias voltage and said second voltage source is the second biasvoltage.
 19. A charge pump as in claim 15, further comprising a firstinverter having an input connected to the first output of the phasedetector and a second inverter having an input connected to the secondoutput of the phase detector, wherein the gate of the fifth transistoris connected to the output of the first inverter and the gate of thesixth transistor is connected to the output of the second inverter. 20.A charge pump as in claim 19, wherein the gate of the fifth transistoris connected to the first output of the phase detector and the gate ofthe sixth transistor is connected to the second output of the phasedetector.